Myofascial edema of gastrocnemius: A prominent MRI characteristic in dermatomyositis patients with anti‐transcriptional intermediate factor 1‐γ antibody

Abstract Aims This study was designed to evaluate the magnetic resonance imaging (MRI) patterns of the lower limb muscles in dermatomyositis (DM) with anti‐transcriptional intermediate factor 1‐γ (anti‐TIF1‐γ) antibody. Methods This retrospective, observational, cross‐sectional study enrolled 12 adult DM patients with anti‐TIF1‐γ antibody. Muscles were assessed for fascial edema, subcutaneous‐tissue edema, muscle edema, and fatty replacement. These features were analyzed in relation to clinical characteristics. Results All 12 patients underwent hip and thigh MRI, and 8 completed calf MRI. All patients showed myofascial edema, muscle edema, and fatty replacement, and 8 out of 12 further exhibited subcutaneous‐tissue edema. Specifically, myofascial edema of the gastrocnemius was observed in all patients (8/8). The vastus intermedialis and vastus lateralis muscles showed the most severe muscle edema, whereas the caput breve of the biceps femoris, semitendinosus, and soleus muscles exhibited the most severe fatty replacement. Although only 1 patient exhibited asymmetric muscle weakness, 9 showed asymmetric muscle edema, and 10 showed asymmetric fatty replacement. Changes in muscle edema positively correlated with creatine kinase (CK) levels. Conclusions Myofascial edema of gastrocnemius was a prominent characteristic of anti‐TIF1‐γ‐positive DM. Early detection of muscle edema, as well as CK levels, may be helpful for monitoring disease activity.


| INTRODUC TI ON
Dermatomyositis (DM) is a specific subgroup of idiopathic inflammatory myopathy (IIM) characterized by proximal muscle weakness and skin lesions. 1,2Anti-transcriptional intermediary factor 1γ (TIF1γ) antibody is considered a DM-specific antibody with a unique clinicopathological phenotype. 3,4Specifically, adult anti-TIF1γ antibodypositive patients can be clinically characterized by proximal muscle weakness, erythematous skin rashes, malignancy, and dysphagia.
4][15][16] Nevertheless, the pattern of muscle involvement by MRI and its association with disease activity in DM with anti-TIF1γ antibody is still warranted.In this study, we analyzed the MRI changes of the lower limbs in a Chinese case series of anti-TIF1γ antibody-positive patients.We further investigated the association between the MRI features and clinical characteristics.

| Study design and patients
This was a retrospective, observational, and cross-sectional study which enrolled 12 adult DM patients with anti-TIF1γ antibody.

Patients were identified from the Department of Neurology at
Qilu Hospital between April 2017 and February 2022.All patients were diagnosed with DM in accordance with the 239th European Neuromuscular Centre International Workshop on DM. 4 This study was approved by the Ethics Committee of Qilu Hospital (Qingdao).
All patients or their guardians provided written informed consent.

| Clinical and laboratory data
Relevant clinical data, including demographics, clinical course, neurological examinations, laboratory data, histopathological data, and treatment regimens, were collected.All patients underwent full screening for malignancy during the diagnostic workup period.Muscle strength was evaluated using the ordinal six-point (0-5) manual muscle testing (MMT) scale, and asymmetric muscle weakness was defined as no less than one grade measured by MMT between the two sides of the same muscle group. 17Patients were followed up about every 2 months after diagnosis.The follow-up time for each patient is added to Table 1.They were primarily followed up for symptoms and signs of muscle weakness, recovery of daily living ability, creatine kinase (CK) levels, and disease recurrence.The MMT grade of the weakest muscle group was used to determine the severity of weakness.Treatment outcomes were graded as follows: no improvement, mild improvement (1 grade in 1-2 muscle groups, continuously requiring help with walking and daily life activities), moderate improvement (>1 grade throughout several muscular groups, requiring little help walking and performing daily activities), marked improvement (symptoms and signs of mild muscle weakness but no functional restriction), or return to baseline (no symptoms or signs of muscle weakness). 18

| Muscle MRI
Lower limb MRI was conducted using a 3 T MRI system (Verio; Siemens Medical Solutions, Erlangen, Germany).The slices were
follows: scale 0, normal appearance; scale 1, mild, interfascicular increased signal intensity; scale 2, mild, intrafascicular segmented increased signal intensity in less than 50% of the volume of the muscle; scale 3, mild, intrafascicular extensive increased signal intensity in more than 50% of the volume of the muscle; scale 4, moderate, intrafascicular segmented increased signal intensity in less than 50% of the volume of the muscle; and scale 5, moderate, intrafascicular extensive increased signal intensity in more than 50% of the volume of the muscle. 19The fatty replacement was

| Statistical analysis
All statistical analyses were performed using the SPSS 26 software.
We conducted a normality test using the Shapiro-Wilk method for all data subjected to statistical analysis.Continuous variables with a normal distribution are expressed as the mean ± standard devia-  1).
After diagnosis at our center, all patients received glucocorticoid therapy, and five also received immunosuppressants.Four patients died during follow-up including two with malignancies, and one was lost to follow-up.Among the remaining 7 patients followed up for more than 16 months (29.1 ± 14.6 months), 6 cases showed marked improvement and 1 showed mild improvement.None of the patients experienced any recurrence.

| Edema of the muscular fasciae and subcutaneous tissue in DM patients with anti-TIF1γ antibody
All 12 patients underwent hip and thigh MRI, and 8 also underwent calf MRI.Before undergoing muscle MRI, five patients were administered methylprednisolone for 2-3 days, while the remaining patients were not administered any glucocorticoids or immunosuppressant therapy.Myofascial edema was found in all patients included in our study (Figure 2A,B,F,I).Among the hip muscles, the obturator internus and obturator externus had the highest proportion (58.3%) of myofascial edema with sparing of tensor fasciae latae and gluteus maximus muscles.Among the thigh muscles, the sartorius, caput longum of the biceps femoris, and semitendinosus showed the highest proportion (58.3%) of myofascial edema.In the calf groups, all eight patients had myofascial edema of the gastrocnemius (caput mediale), and none had myofascial edema of the flexor hallucis longus (Figures 2A,F,I and 3).Moreover, eight patients showed edema of the subcutaneous tissue, with one in the hip, seven in the thigh, and five in the calf (Figure 2D,E,H).

| Muscle edema in DM patients with anti-TIF1γ antibody
All 12 enrolled patients had muscle edema in the lower limbs, and most muscles showed an edema scale of 2-3 (Figures 2B,C,G-I and 4A-C).Among the hip muscles, the obturator internus and the obturator externus had the most severe edema.Among the thigh groups, the anterior compartment had the most severe edema, followed by the medial and posterior compartments.Specifically, the vastus intermedialis and vastus lateralis showed the most severe edema, whereas the caput longum and breve of the biceps femoris and semimembranosus were relatively spared.Among all the calf muscles, the caput mediale and caput laterale of the gastrocnemius were relatively spared, whereas the other groups were similarly affected (Figure 4A-C).Asymmetric muscle edema was found in nine patients, including one with asymmetric muscle weakness (Figure 2G,H).No cases of muscle attachment point edema were observed.

| Correlations between MRI changes and clinical data
A positive correlation was found between the edema score of the posterior compartment of the thigh muscles and disease duration  2).No significant relationship was found between MRI changes including muscle edema and fatty replacement and treatment outcomes (p > 0.05) (Table S1).There was no significant correlation between fatty MRI changes including the global score of fatty replacement, scores of each compartment, and clinical manifestation including age at onset, disease duration, and CK levels (p > 0.05) (Table 2).
Besides, there was no statistically significant difference in the fatty and edema scores of muscle groups between patients with tumors and those without tumors (p > 0.05, Table S2), and no difference was found between these two groups in field of the frequencies of myofascial edema and subcutaneous-tissue edema.

| DISCUSS ION
This is the first study to evaluate the pattern of edema and fatty replacement changes of anti-TIF1γ antibody-positive patients in a Chinese case series.Overall, we find that myofascial edema of the gastrocnemius was a prominent MRI characteristic of anti-TIF1γ-positive DM.Our analysis also showed that these anti-TIF1γpositive patients showed a distinct pattern of muscle edema and fatty replacement changes of lower limbs with common asymmetric pattern in MRI.The vastus intermedialis and vastus lateralis showed the most severe muscle edema, while the tensor fasciae latae, biceps femoris, semitendinosus, and soleus muscles showed the most severe fatty replacement.
Anti-TIF1γ antibody is a multifunctional protein related to immunoregulation, cell cycle, and transcription of a tumor suppressor gene. 22This antibody has a relatively high frequency (approximately 25%) in adults with DM and is closely associated with malignancy. 3,5,23In our study, three of the enrolled patients (25%) showed malignancy, and two (67%) died during follow-up.In view of the high prevalence of malignancy in patients with anti-TIF1γ-positive DM and the poor prognosis in patients with malignancy, the early diagnosis of anti-TIF1γ-positive DM is very important.Unfortunately, among patients with anti-TIF1γ antibody, MRI features were not correlated to malignancies.Since myofascial edema of the gastrocnemius was found in all our tested patients and a high frequency of gastrocnemius myofascial edema was not reported in any other group of IIMs, we assumed that this unique MRI finding could be helpful in the early diagnosis of anti-TIF1γ antibody-positive DM to monitoring malignancy occurrence.
All of the patients included in our study had myofascial edema, consistent with previous findings that high signal intensity of the fascia is a characteristic MRI feature of DM. 24,25 We further detected the unique pattern of myofascial edema in patients with anti-TIF1γ antibody as prior studies did not focus on the myofascial edema patterns of each kind of MSA.Specifically, myofascial edema of the calf muscles was found in all of our patients, while myofascial edema of the hip and thigh muscles was also found in most patients.Since most of our patients with anti-TIF1γ antibody showed perifascicular changes as reported, we inferred that the high frequency of myofascial edema involvement in anti-TIF1γ antibody-positive DM may correspond to the obvious perifascicular damage in muscle biopsy. 5,8The remarkable myofascial edema This view was supported by another report in China, which found that patients with anti-synthetase syndrome (ASS) characterized by perimysial connective tissue in muscle pathology also exhibited frequent myofascial edema. 9Indeed, the pattern of myofascial edema was significantly different between the two subgroups.
Specifically, patients with ASS usually showed myofascial edema of the tensor fasciae latae, while our patients with anti-TIF1γ antibody showed myofascial edema of gastrocnemius without tensor fasciae latae involvement. 9This difference may be useful for distinguishing between two similar subgroups.
Unlike IIMs with antibodies to signal recognition particle (SRP) which show more pronounced edema than fatty replacement, no significant difference was shown between the degree of fatty replacement and muscle edema in patients with anti-TIF1γ antibody. 15Moreover, the patterns of fatty replacement and muscle edema differed between the two groups.Specifically, the vastus lateralis, rectus femoris, biceps femoris, and adductor magnus were the muscles of most severe edema affected in anti-SRP myopathy, while the vastus intermedialis and vastus lateralis were the most affected in DM patients with anti-TIF1γ antibody. 15The most severe fatty replacement muscles were the hamstrings and adductor magnus in anti-SRP myopathy, while the biceps femoris and semitendinosus were the most affected in anti-TIF1γ antibody-positive DM.
The different MRI findings between these two subgroups support our finding that each type of MSA has unique MRI characteristics.
Strikingly, asymmetric MRI pattern was common in our anti-TIF1γ antibody-positive patients.Unlike inclusion body myositis with marked asymmetric involvement, most patients show subclinical asymmetric muscle weakness. 26Since patients with ASS and patients with immune-mediated necrotizing myopathy also showed bilateral asymmetry in previous reports, we assumed that the involvement of the muscle groups was not strictly symmetrical in IIM.

TA B L E 2
The correlation analysis between muscle MRI changes and clinical data.
According to the schedule, patients who had disease recurrence required reexamination of muscle MRI again and adjustments for medical intervention.The research flowchart of our study is shown in Figure S1.Normal serum creatine kinase (CK) levels ranged from 38 to 174 U/L.Anti-TIF1γ antibody antibodies were detected in all patients by immunodot assay (Autoimmune Myositis Profile Antibody IgG Detection Kit MT559, MyBiotech Co., Ltd, Xi'an, China), according to standard methods.Muscle biopsies were taken from the biceps brachii, deltoid, or quadriceps of all 12 involved patients positive for anti-TIF1γ antibody.Serial frozen sections were stained with hematoxylin and eosin (HE), anti-CD3 mouse monoclonal antibody (clone LN10; Zhongshan Golden Bridge Biotechnology, China), anti-CD8 rabbit monoclonal antibody (clone SP16; Zhongshan Golden Bridge Biotechnology), anti-MHC-I rabbit monoclonal antibody (clone EP1395Y; Abcam, UK), anti-MHC-II mouse monoclonal antibody (clone CR3/43; Dako, Denmark), antimembrane attack complex (MAC) mouse monoclonal antibody (clone aE11; Dako), and anti-MxA rabbit polyclonal antibody (Polyclonal, Abcam).Perifascicular necrosis/regeneration, perifascicular atrophy, and the expression of autoimmune markers, including MHC-I, MHC-II, MAC, and MxA, with perifascicular enhancement were all regarded as perifascicular changes.
evaluated on T1 sequences according to the modified Mercuri's scale as follows: scale 0, normal appearance; scale 1, scattered distribution of increased signal intensity; scale 2, areas of confluent increased signal intensity in less than 30% of the volume of the muscle; scale 3, areas of confluent increased signal intensity in 30%-60% of the volume of the muscle; scale 4, areas with confluent increased signal in more than 60% of the volume of the muscle; and scale 5, muscle entirely replaced by areas of confluent increased signal.20,21Indeed, firstly we evaluated the edema score of each muscle group through the axial position.The scores at the proximal and distal ends were recorded separately.If there was a discrepancy between the scores of the proximal and distal ends, we counted the number of layers affected by the different scores and set the score with the more affected layers as the final edema score of the muscle.Finally, we evaluated the overall edema of this muscle in the sagittal position to ensure the reliability of the edema score.In this study, we examined the skeletal muscle, muscular fascia, and subcutaneous tissue of the lower limbs, including the muscles of the hip, thigh, and calf.The hip muscles were divided into the following segments: (1) the anterior compartment (tensor fascia latae) and (2) the posterior compartment (gluteus maximus, obturator internus, obturator externus, and quadratus femoris).Similarly, the thigh muscles were divided into (1) the anterior compartment (sartorius, rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius), (2) the medial compartment (gracilis, adductor longus, adductor brevis, and adductor magnus), and (3) the posterior compartment (caput breve and caput longum of the biceps femoris, semimembranosus, and semitendinosus).The calf muscles included (1) the anterior compartment (tibialis anterior, extensor hallucis longus, and extensor digitorum longus), (2) the lateral compartment (peroneus longus and peroneus brevis), and(3) the posterior compartment (caput mediale and caput laterale of the gastrocnemius, soleus, tibialis posterior, flexor hallucis longus, and flexor digitorum longus).An asymmetric MRI pattern was defined as no less than one scale between the two sides of the same muscle group.Magnetic analysis of MRI image was performed by a musculoskeletal radiologist (JH) and a neurologist (CZ) blinded to the demographic and clinical features.In muscles with different edema and fatty replacement scores, the two readers reviewed the muscles together to agree on the final score.

All 12 enrolledF I G U R E 1
patients had fatty replacement, with all displaying varying degrees of fatty replacement among the different muscle groups (Figures2J-L and 4D-F).Among the hip muscles, the tensor fasciae latae and gluteus maximus muscles showed the most severe fatty replacement.Among the thigh muscles, the caput breve of the biceps femoris and semitendinosus muscles showed the most severe fatty replacement, whereas that of the rectus femoris was relatively spared.The soleus exhibited the highest fatty replacement, followed by the caput mediale and caput laterale of the gastrocnemius in The perifascicular changes of muscle biopsy in patients with anti-TIF1γ antibody.(A) Perifascicular atrophy in Patient 3. (B) Perifascicular necrosis in Patient 6. (C) Perifascicular enhancement of MHC-I in Patient 3. (D) Perifascicular enhancement of MHC-II in Patient 3. (E) Perifascicular enhancement of MAC in capillary in Patient 7 (black arrow).(F) Perifascicular enhancement of MAC in sarcolemma in Patient 6 (black arrow).Scale bars = 50 μm.MAC, membrane attack complex; MHC, major histocompatibility complex class; and TIF, transcriptional intermediate factor.calf muscles (Figure 4D-F).Asymmetric fatty replacement was observed in 10 patients, including 1 with asymmetric muscle weakness (Figure 2J,K).Moreover, correlation analysis showed that the degree of muscle edema and fatty replacement in the lower limbs were not parallel (p > 0.05) (Figure 4C,F).

F I G U R E 2
Typical muscle MRI manifestations of patients with anti-TIF1γ antibody.(A, D, G, J) The MRI manifestations of Patient 1. (B, E, H, K) The MRI manifestations of Patient 5. (C, F, I, L) The MRI manifestations of Patient 3. (A) (Coronal STIR), obvious myofascial edema of gastrocnemius, soleus, and peroneus longus is shown (white arrowheads).(B) (Coronal STIR), obvious myofascial edema of the sartorius (white arrowheads) and diffuse edema in the vastus lateralis and vastus intermedius (red stars) are observed.(C) (Coronal STIR), diffuse edema in the gracilis, semimembranosus, and semitendinosus is observed (red stars).(D) (Coronal STIR), diffuse subcutaneous-tissue edema is observed in the left medial thigh.(E) (Coronal STIR), bilateral symmetrical honeycomb-like edema of subcutaneous tissue of thigh is shown (white arrows).(F) (Coronal STIR), remarkable myofascial edema of gastrocnemius is observed (white arrowheads).(G) (Axial SPAIR), muscle edema is observed in anterior compartment of the thigh muscle, and that is more severe on the left side (red stars), while the posterior compartment is relatively spared (red #s).(H) (Axial FS) Obvious edema in the anterior compartment of the thigh muscle is observed (red stars), which is more severe on the right side, while the posterior compartment is relatively spared (red #s).Remarkable subcutaneous-tissue edema is shown (white arrows).(I) (Axial T2-FS), remarkable myofascial edema of gastrocnemius is observed (white arrowheads), and muscle edema of the anterior compartment showed a honeycomb-like appearance (solid line box).(J) (Axial T1WI), the fatty infiltration of the left semimembranosus is severe (red dashed lines), while it is moderate on the right side.(K) (Axial T1WI), the fatty infiltration of the right medial compartment of the thigh muscle is severe, with complete replacement of the right gracilis, adductor longus, and adductor brevis muscles by lipids.However, the medial compartment of the left thigh is relatively spared.L (Axial T1WI), fatty infiltration is not evident in the anterior compartment of the calf muscles (red stars).FS, fat saturation; MRI, magnetic resonance imaging; SPAIR, spectral attenuated inversion recovery; STIR, short-tau inversion recovery; TIF, transcriptional intermediate factor; and T1WI, T1-weighted imaging.(p = 0.048, r = 0.581).Moreover, edema changes, including the global edema score of the thigh muscles, the edema score of the medial compartment of thigh muscles, the global edema score of calf muscles, and edema score of the posterior compartment of calf muscles, were positively correlated with CK levels (p = 0.015, r = 0.678; p = 0.001, r = 0.832; p = 0.045, r = 0.719; and p = 0.017, r = 0.80, respectively) (Table

F I G U R E 3 F I G U R E 4
The percentage of myofascial edema in the lower limb muscles of dermatomyositis patients with anti-TIF1γ antibody.TIF, transcriptional intermediate factor.The severity and distribution of muscle edema and fatty replacement in the lower limbs of dermatomyositis patients with anti-TIF1-γ antibody.(A) The score for the degree of muscle edema of the left lower limbs (longitudinal axis depicts the percentage of scores across different levels).(B) The score for the degree of muscle edema of the right lower limbs.(C) The mean Stramare scale for muscle edema of lower limb muscles.(D) The score for the degree of fatty infiltration in the muscles of the left lower limbs.(E) The score for the degree of fatty replacement in the muscles of the right lower limbs.(F) The mean Mercuri' scale for fatty replacement of lower limb muscles.TIF, transcriptional intermediate factor.changes potentially implied the important role of perifascicular changes in the pathogenesis of anti-TIF1γ antibody-positive DM.